Analytical instruments are useful in performing research, testing, diagnostics and other types of work. Analytical instruments 10 may operate in the space domain as illustrated in FIG. 1A, or in the time domain as illustrated in FIG. 1B.
As illustrated in FIGS. 1A and 1B, analytical instruments 10 typically employ three fundamental components: a source 12, a disperser 14; and a detector 16. The source 12 typically takes one of two forms: i) emitting a sample to be tested, or ii) emitting a probe in the form of particles (e.g., ions) or waves (e.g. electromagnetic radiation or sound). The disperser 16 also typically takes one of two forms: i) a discrete dispersing element, or ii) the sample itself dispersing the probe particles or waves. The disperser 14 disperses the sample or probe in time or space. The detector 16 also takes one of two forms: i) detecting the sample, or ii) detecting the probe particles or waves, as a function of time or space. The detector 16 produces a detector signal as a function of detected time or detected position, which is referred to as a “spectrum” and which provides information about the sample being tested.
FIG. 2A shows an example of a conventional analytical instrument in the form of a Wiley-McLaren-type time-of-flight mass spectrometer (Wiley and McLaren 1955), where a sample of ions is dispersed in time according to ion mass-to-charge ratio. FIG. 2B shows another example of a conventional analytic instrument in the form of a Czerny-Tumer-type optical monochromator, where light is dispersed in space according to its wavelength.
In general, the design of analytical instruments is governed by scaling laws, describing how changes in parameters like the size of the source, the size of the dispersing element, the resolution, and the sensitivity are interrelated. In most cases, the resolution improves as smaller sources (for position sensitive detection) or shorter pulses (for time sensitive detection) are used. In the case of the Wiley-McLaren-type time-of-flight mass spectrometer, illustrated in FIG. 2A, the resolution is proportional to the length of the flight path. Therefore, resolution can be improved by enlarging the instrument if the dimensions of the ion source are fixed. In the case of the Czerny-Turner-type optical monochromator, illustrated in FIG. 2B, sensitivity is proportional to the optical aperture of the instrument, again favoring the design of large instruments.
Miniaturization of analytical instruments, which is highly desirable based on considerations such as cost and portability, often requires the circumvention of these scaling relations, since otherwise device performance is reduced to an unacceptable low level. A prominent problem stemming from miniaturization is the reduction of sample volume or intensity, due to the smaller source, causing a proportionally reduced signal at the detector and thus a reduced signal-to-noise ratio, if the noise stems mainly from the detector, as is often the case. Thus, there is a need for miniaturized analytical instruments with relatively good signal-to-noise ratios. There is also a need for conventionally sized analytical instruments with higher signal-to-noise ratios than found in typical existing analytical instruments.